CDI ConversationScoped long-running Bean not worki

问题:

I got some problems understanding the Conversation scope of Weld or CDI.

In my JSF Faclets page i call:

        <f:metadata>
            <f:event type="preRenderView" listener="#{viewBean.start}" />
        </f:metadata>

The bean:

import javax.enterprise.context.Conversation;
import javax.enterprise.context.ConversationScoped;
@Named
@ConversationScoped
public class ViewBean implements Serializable {

@Inject
    private Conversation conversation;

public void start() {
    if (conversation.isTransient()) {
        System.out.println("START CONVERSATION");
        conversation.begin();

    }
}

Now every time I refresh my browser, a new Conversation is started. Is that the correct behaviour? So why is the conversation always transient? No exception is thrown. The beans.xml is created and empty:

<beans xmlns="http://java.sun.com/xml/ns/javaee"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/beans_1_0.xsd">
</beans>

回答1:

Short answer: Yes, this is the correct behavior.

Long answer: A conversation represents a "unit of work", which a such has to be demarcated explicitly. This is done with the explicit call of conversation.begin() - as you are doing already. Should you want to use the same conversation over more than one request, you have to propagate it - this is what you are not doing :-)

When you propagate a conversation, a conversation-id is appended to the request. This tells the container which conversation is wanted. When you just hit the refresh button without a conversation-id in your request a new conversation is generated for each request.

From the documentation:

The conversation context automatically propagates with any JSF faces request (JSF form submission) or redirect. It does not automatically propagate with non-faces requests, for example, navigation via a link.

If you need to propagate it manually, just add the conversation-id to the request:

<h:link outcome="/addProduct.xhtml" value="Add Product">
   <f:param name="cid" value="#{javax.enterprise.context.conversation.id}"/>
</h:link>

All that and much more is explained here.